Programmable assembly apparatuses, often known as robots, are generally controlled by a computer, and move in a pre-set pattern to accomplish whatever assembly task is required. Rapid advances in microprocessor technology and electronics have led to increasing sophistication in programmability, and greater flexibility and complexity in the tasks that robots can accomplish. However, a mechanical gripping device of some sort is still necessary at the interface between the robot and the object that is to be manipulated. A greater potential in programmability is useless without such a device that is capable of translating that potential into physical results.
Several different types of mechanical gripping devices are known. One relatively simple type uses a gripper that operates like a pair of tongs, with a pair of members that move together and apart. Such a gripping device is clearly limited in the types of tasks that it can perform, and does not have the flexibility to manipulate objects of widely varying size or shape. Another type uses a more complex gripper with a pair of articulated fingers, each including two or more serially pivoted elements, that can better conform to objects of varying size and shape. An example of this type is disclosed in the U.S. Pat. No. 4,350,381 to Hellmann, in which the articulated finger elements are powered by hydraulic means. Another type of gripper with an articulated finger has serially pivoted finger elements operated by a series of pulleys and cables. Pulling on one cable causes the finger to wrap or conform to an object, the finger elements acting in series, one after another. An antagonistically acting cable unwraps the finger elements in reverse order. An example of this type of gripping device is disclosed in NASA Technical Briefs, Fall 1983, page 99. A drawback of this type of device is that it operates in only a single mode, that is, all the finger elements wrap an object, and then all are unwrapped. The finger elements cannot be operated selectively. Such devices are also more complex and less compact than may be desirable in many manufacturing operations.